1. Field of the Invention
The present invention generally relates to analog-to-digital converters and it particularly relates to an analog-to-digital converter for converting input analog signal into digital signal through multiple conversion processings.
2. Description of the Related Art
With the development of the digital signal processing technologies, analog-to-digital converters (hereinafter referred to as “A-D converters”) are increasingly mounted on various equipment and devices such as digital still cameras, digital movie cameras and mobile phones. One of kinds of A-D converters that excel both in conversion speed and conversion accuracy is a pipeline-type A-D converter.
The pipeline-type A-D converter is provided with a plurality of stages each of which is provided with a sub-A-D converter circuit. Each stage is provided with an amplifier circuit for amplifying a residual signal (obtained after the removal of a digital component converted by a sub-A-D converter circuit from an input signal to its own stage) and a sample-and-hold circuit for sampling and holding this input signal. The amplifier circuit and the sample-and-hold circuit generally include operational amplifiers as their circuit components, so that an offset voltage for the operational amplifier needs to be taken into account.